Method of and apparatus for determining ion concentration



Oct. 28 1924.

H. C. PARKER METHOD OF AND APPARATUS FOR DETERMINING IoN CONCENTRATIONFiled May 16, 1924 mi fi i H. s I m M M m ,u. I m w u w w w INVENTOR 7as. 652% 1A TTORNEY concentration. I

My invention resides in the method, ap-

Patented Oct. 28, 19 24.

UNITED STATES HENRY o. PARKER, or, PHILADELPHIA,

PENNSYLVANIA, ASSIGNOR TO NORTHRUP COMPANY, OF PHILADELPHIA,PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

METHOD OF AND APPARATUS FOR DETERMINING ION CONCENTRATION.

.1 Appilication filed May 16, 1924. Serial No. 713,683.

' v p To all whom at may concern:

Be it known that I, HENRY C. PARKER, residing in the city and county ofPhilavented certain new and useful Improvements in Methods ofand"Apparatus for Deter-.

mining Ion Concentration, of which the following is a specification. 9

My invention relates to the measurement or determination of theconcentrations of selected ions, as hydrogen or hydroxyl ions, insolutions or electrolytes, and in general to the utilization for anypurpose of the electro-motivc-force dependent upon or representative ofion concentrations.

, In accordance with my invention, there is utilized and provided anoxygen electrode, suitable particularly foralkaline and weak acidsolutions, including such as contain oxidizing substances in solution,having such characteristics that when employed with a suitable constanthalf cell; the equation expressing the relation between theelectromotiveforce of the cell and the logarithm of the reciprocal ofthe ion concentration is a linear function, that is, the curve yieldedby plotting electro-motive-forces of the cell against the logarithm ofthe reciprocals of the ion concentration is astraight line.

In 'accor'dance'with my invention, such an oxygen electrode comprises anelectrode of suitable metal or other material, disposed adjacent or inintimate contact with a solid which yields oxygen ions in suflicientquantity or at suitable rate and which is insoluble or at most slightlysoluble in the solution involved.

In accordance with my invention, the oxygen electrode may comprise anelectrode of metal or other suitable material immersed in the solutionto which there has been added I a solution of oxidizing material ormaterial yielding oxygen ions, to effect a constant and definiteconcentration of oxidant in the so-' lution.

Further in accordance with my invention, there is provided a constanthalf cell comprising an electrode of suitable metal immersed in asolution of a suitable compound or salt of the metal of preferablyconstant paratus and combinations of materials of, the characterhereinafter described and claimed. delphia, State of Pennsylvania, have.in-

For an understanding of my method and for an illustration of some of thevarious forms my apparatus may take, reference is .to be had to theaccompanying drawings, in which:

Fig. 1' isaside elevational view, partly in vertical section, ofapparatus embodying my invention, in association with a diagrammaticview of a circuit in which it is utilizable.

Fig. 2 is a side elevational view, partly in vertical section, ofapparatus utilizable for introducing into the electrolyte solution atsuitable rate or in suitable quantity a solution of an oxidant.

Heretofore, in the art of measuring, determining or utilizing ionconcentration, as of hydrogen or hydroxyl, there has been commonlyemployed a ydrogen electrode which has the characteristic that therelation between the electro-motive-force of the cell and the logarithmof the reciprocal of the ion concentration is a linear function.However, there are some relations in which a hydrogen electrode isunsuitable, as for exam le, when the solutionv contains o-xidiz-,

tween the theoretically and experimentally determined values of thepotential of the cell provided with such an electrode, and also becausethe potential drifts and 'approaches or attains no definite value ormagnitude as a limit.

It is also known that various metallic electrodes immersed in a solutionwhich is or has been in contactw ith the air give a rough there .existsa considerable difierence be-' measurement of hydrogen ion concentrationdue, presumably, to a small but variable or indefinite amount of oxygendissolved in the solution, and thereby causing them to func metallicelectrodes,-so employed, yield inaccurate results. When the metallicelectrode is polarized by passing a small current 1100' tion in a senseas oxygen electrodes. Such through it for a suitable time, as a fractionof a minute, the magnitude of the potential thereafter produced by theelectrode differs considerably from the true equilibrium potential ofthe'electrode. This is shown by polarizingthe electrode by passingacurrent of the same magnitude through it in opposite direction, afterwhich the potential obtained will be considerably different from thatfirst mentioned. The difference between these two potentials may betermed a dead space, and within this range or dead space the electrodeis found to be substantially entirely insensitive to changes in hydrogenion concentration. ln investigating electrodes of Y many differentmetals, including tungsten,

it is found that this dead space varies between .005 and .090 volt forthe diiferent metals. For tungsten the dead space or range is of theorder of .005 volt, which limits its accuracy and hence its field of ap;plicability. The relation of the potential of the tungsten electrode tothe logarithm of I the hydrogen ion concentration is a curve of which isinvolved, as for measurement or determination, is delivered into thelower end of the vessel or tube 1, of glass or other suitable material,and passes therefrom through the tube 2. 'lmmersed in the elec trolytein the chamber 1 is the negative or oxygen electrode N connected throughthe conductor -3 and galvanometer G with the contact l slidable alongthe resistance R comprised in a potentiometer with the adjustableresistance R and the battery or other source of uni-d rectional currentB. The positive electrode P is connected through conductorwith theresistance R, and connected between the contact 4 and conductor 5 is thevoltmeter V.

As well understood in the art, the current from the source B flowingthrough the resitance R is adjusted to suitable or predeterminedmagnitude by adjusting the resistance R The cell, comprising theelectrodes P and N, produces an electro-motive-force dependent upon themagnitude of the hydrogen or hydroxyl ion concentration in theelectrolyte passed through the chamber 1, and this eIectro-motive-forceis determined by movmg the contact 4 to such position along the missesresistance R that the deflection of the galvanometer G isnil, whereuponthe electro-motive-force of the cell is readable upon the voltmeter V.

The electrode N is preferably of'tungsten, though it may be of platinum,gold, palladium, or other suitable metal or conductingmateriaL'preferably neutral to the solution in which immersed, andhaving suitably high conductivity or low specific resistance. Theelectrode maybe in the form of wire as indicated,or in any othersuitable form.

The electrode material N is disposed suitably adjacent to or in intimatecontact with the body ()-of such character or composition as to yieldoxygen or oxygen ions in suflicient quantity or at sufiicient rate toproduce the effects herein described, including the avoidance orelimination of the aforesaid dead space. The oxygen or oxygen ionsyielded by the material 0 saturates the solution adjacent or in theneighborhood of the electrode N with oxidant whose .concentration in thesolution is constant and definite.

The material 0 is a solid, slightly, it at all, soluble in theelectrolyte solution involved, and consisting of or to suitable degreecomprising material yielding at desired rate or in suflicient quantityoxygen or oxygen ions which efiect or intimately contact with theelectrode N.

- In the example illustrated, the body 0 is formed of granular or finelysubdivided oxygen-yielding material mixed with collodion or othersuitable binder and rolled or otherwise ap lied in a layer upon theexterior of the tu e or member 6, of glass or other suitable material,and there is then wound upon the coating 0 the electrode wire N. whichis sealed through the lower end of the tube 6 at 7 and is eitherconnected directly to the conductor 3 or contacts 'within the tube 6with a body of mercury S with which the conductor 3 connects. The tube 6extends through a rubber or other stopper 9 and supports the electrodestructure in the solution.

For the oxidant 0 there may be used various oxides or a. mixtureofoxides. For example, there may be used manganese dioxide, cobalticoxide, lead dioxide, and equivalents. I

lln general, the highest or higher oxides of suitable metals arepreferred, for it has been found that the metal oxides containing thelargest proportion of oxygen effected to greatest extent the eliminationof the aforesaid dead space.

Various mixtures of the higher and lower oxides of a metal, preferablyother than the metal of which electrode N is composed, may also beemployed and efi'ect excellent results. For example, there may beemployed manganese dioxide inmixture with sesquioxide Illltli utilized asuitable natural mineral, such, for

' metal or a mixture of higher and lower of manganese; cobaltic inmixture .with cobaltous oxide; lead dioxide in mixture with either orboth litharge and redoxide of'lead; or a mixture of litharge and redoxide of lead. Or with the oxide of one metal may be mixed an oxide ot adifferent oxides of a difi'erentmetal or a mixture of oxides ofdifferent metals.

For the oxidizing body '0 there may be example, aspyrol'usite, whichalone is unsuitable because of variation in effects obtained therewith,probably due-to its high specific resistance and non-uniformity ofdifferent samples. But when there is employed on or closely adjacent topyrolusite a tungsten or other metallic electrode N, the

combination serves to attain the uniformv and desired results andeffects herein described,

There is combined in the same structure with the electrolyte containerand'the negative, electrode a constant halfcell. In the exampleindicated, the half cell comprises the glass tube 10, within which isdisposed the positive electrode P of suitable metal in any suitabl form,such as a grid, wire, or the like, with which the conductor 5 connects.

The electrode P may be of copper, in which case there will be passedthrough the tube 10 through its lower end a solution which flows ofcopper sulphate of preferably constant concentration. Or there" may beused for the electrodeP any other suitable metal with which there willbe used an appropriate electrolyte comprising a solution of-constantconcentration of a suitable .salt of the metal. For example, theelectrode P may be of nickel, in which case the electrolyte associatedtherewith may be nickel sulphate, nickel chloride, or equivalent, ofconstant concentration. In any case, a constant difference of potentialis maintained between the electrode P and its co-acting solution,gradually upward through the tube and through the restricted orifice orpassage 11 into the electrolyte flowing from the vessel 1 charged fromthe latter. The potentialat the liquid junction at 11 is'small andconstant, with the result that GTange in electromotive-force occurs onlyat theelectrode N in accord with changeof hydrogen or hy-.

droxyl ion concentration.

In somecas'es the solution or electrolyte containing the ions whoseconcentration is to be measured or determined or otherwiseuti- .lizedcontains reducing agents or substances in such quantity or of suchpower,such, for example, as nitrites, that the amount of, oxy gen, supplied bythe body 0 is insuflicient. In such" cases it is desirable to supplyoxygen through the tube 2 and 'disin such quantity that the nitrites orto supply ample oxygen ions to the negative electrode N to maintain andproduce the effects and results herein described, including theelimination of the aforesaid dead space.

For this purpose there may be introduced into the solution orelectrolyte under investigation a soluble or dissolved oxidizing agent,therefore effecting mixture with the solution under investigation, andin this mixture is immersed the negative electrode N of tungsten orother suitable material in the form of a wire, gauze or plate, with orwith; out'tlie co-action of a body 0.

It has been found'that the potential of such an electrode varies to someextent with the number of oxygen ions in or with the oxidation potentialof the solution. It is essential, therefore, that this concentration,

14 is maintained constant by the overflow 15.

In a bottle or equivalent receptacle 16 there is stored a solution ofoxidant or oxidizing agent, for example hydrogen peroxide, of suitableor predetermined concentration.-

. be kept constant in order that the electrode The tube 17 extends intothe receptacle 18in which the solution of oxidant is maintained at asubstantially constant level 19, below which the outlet of the tube 17extends. Air bubbles can enter the vessel 16 only when the solution hasfallen below the outlet opening of the tube 17, and accordingly apartial vacuum is-maint-ained in the bottle 16 which prevents the liquidfrom rising above the constant level 19. Thesolution of oxidant flowsthrough the restricted passage or capillary tube 20, which permits a fewdrops per minute to be delivered into the solution or electrolytepassing from the chamber 13 throughthe outlet 21, which may be connectedto the inlet at thelower end of the ves 'sel 1 of Fig. 1. Accordinglythere is delivered to the'structure of Fig. 1 a mixture of the solutionor electrolyte under investiga tion with 'a solution of oxidant presentvin substantially constant amount or concentration, since the solutionin the vessel 16 is of predetermined or suitable ctfidentration and isdelivered at substantially constant rate, due to the constant differencein levels 14 and 19,-in-to the solution under investigaderinvestigation, such as boiler teed wamr, or any other like solution,leaving'sufiioient oxygen to efi'ect co-operation with the electrode Nof the character herein described, eliminating the dead space andaccordingly effecting true results in accord with variations of hydrogenorhydroxyl ion concentration.

It is readily seen of course that the addition of a solution of oxidantin a definite and constant concentration as described above accomplishesthe desired result (namely the bringing in contact with the electrode ofa definite and constant concentration of oxidant) in a different mannerfrom the method where a solid oxidant is employed. In the latter casethe solution in the neighborhood of the electrode is kept saturated withthe nearly insoluble oxidant and hence is kept at a constantconcentration; while in the former case the concentration of oxidant ismaintained by introducing it at suitable rate into the solution.

Reference in the appended claims to hydrogen ions will be understood,for brevity, to include hydrogen, hydroxyl, and such other ions to theutilization or determination of the concentration of which my'inventionis applicable.

What I claim is: p

1. lln the production of an electro-motiveforce representative of theconcentration of hydrogen ions in a solution, the method which compriseseffecting in said solution in contact with an electrode a substantiallyconstant and definite concentration of oxidant.-

2 lln the production of an electro-motiveforce representative of theconcentration of hydrogen ions in a solution, the method which compriseseffecting in said solution in contact with an electrode a substantiallycon stant and definite concentration of oxidant of such magnitude astocause a linear rela-' tion between the logarithms of the recipro calsof the hydrogen ion concentrations and the potentials 0t said electroderepresenting said concentrations.

3. In the production of anelectro-motiva force representative of theconcentration of hydrogen ions in an alkaline or weak acid solution,.the method which comprises efiecting in said solution in contact withan electrode a substantially constantand definite concentration ofoxidant of such magnitude as to cause a linear relation between thelogarithms of the reciprocals of the hydro gen ion concentrations andthe potentials of said electrode representing said concentrations. v

4:. In the production of an electro-motiveforce representative of theconcentration of hydrogen ions in a solution containing a reducingagent, themethod which comprises introducing into cals of the hydrogenthe potentials representing s d comment-f3 the solution oxidant inquantity suiiicient to efiect after oxidation of the reducing agent asubstantially constant and definite concentration of oxidant.

5. in the production or an electro-inotivei'orce representative of theconcentration of hydrogen ions in a solution containing a reducingagent, the method which comprises introducing into the solution oxidantin quantity sufiicient to effect after oxidation of the reducing agent asubstantially 0011- stant and definite concentratioii of oxidant of suchmagnitude as to cause a linear relation between the logarithms of thereciproion concentrations and tions and effected solution. 1

6. ln the production of an electro-motiveforce representative of theconcentration of hydrogen ions in a solution, the method. whichcomprises bringing the solution into contact with an electrode,effecting in the solution adjacentsaid electrode a substantiallyconstant and definite concentration of oxygen ions, and producingsaidoxygen ions by an; electrode in a solid oxidant immersed in saidsolution. 7. A cell for utilizing or determining concentration ofhydrogen ions in a solution comprising an electrode, and means foreilecting a substantially constant and definite concentration of oxidantinsaid solution. I

8. A cell for utilizing or determining concentration of hydrogen ions ina solution comprising an electrode, and means for delivering into thesolution. a dissolved oxidant to eilect in said solution a substantiallyconstant and definite concentration of oxidant.

means for passing therethrougli a solution containing hydrogen ions, avesselcontaining a solution of oxidant, and means for delivering saidlast named solution into said first named solution to effect in saidfirst named solution asubstantially constant and definite concentrationof oxidant, and an electrode immersed in said solution in saidcontainer.

I0. The combination with a container, of

means for passing therethrough a solution containing hydrogen ions, avessel containing a solution of oxidant,*means for. delivering said lastnamed solution into said first named solution to effect in said firstnamed solution a substantially constant and definite concentration ofoxidant, and a tungsten electrode immersedin said solution in saidcontainer.

11. An oxygen electrodefor a hydrogen ion cell comprising an electrode,and adjacent said electrode a solid yielding oxygen ions. J

12. An oxygen electrode for a hydrogen ion cell comprising a mass ofsolid oxidant,

9; The combination with a container, of

therewith.

.14. An oxygen electrode for a hydrogen ion cell comprising a mass ofsolid oxidant, and a conductor wrapped upon said mass.

15. An oxygen electrode for a hydrogen ion cell comprising a mass ofsubdivided solid oxidant and a binder, and an electrode associatedtherewith.

16. An oxygen electrode for a hydrogen ion cell comprising a mass ofsubdivided solid oxidant and a binder, and an electrode incontacttherewith.

' 17. An oxygen electrode for a hydrogen ion cell comprising a support,a coating of subdivided solid oxidant and binder on said support, and anelectrode adjacent said coat- 18. An oxygen electrode for a hydrogen ioncell comprising a support, a coating of subdivided solid oxidant andbinder on said support, and an electrode in contact with said coating.

19. An oxygen electrode for a hydrogen ion cell comprising a mass ofpyrolusite, and an electrode in contact therewith.

20. An oxygen electrode for a hydrogen ion cell comprlsing a mass ofpyrolusite, and a tungsten electrode in contact therewith.

2-1. An oxygen. electrode for a hydrogen ion cell comprising a tungstenelectrode, and adjacent said electrode a solid yielding oxygen ions. 7 V

22. An oxygen electrode for a hydrogen ion cell comprising a mass ofsolid oxidant,

and a tungsten electrode so positioned with respect thereto that thesolution contacting with said electrode is substantially saturated withoxygen ions.

I 23. An oxygen'electrode for a hydrogen ion cell comprising a mass ofsubdivided 'mletallic solid oxides of a concentrations 0 solid oxidantand a'binder, and a tungsten electrode in contact therewith.

24; An oxygen electrode for a hydrogen ion cell comprising an electrode,and adjacent said electrode a mixture of difl'erent metallic solidoxides. r

25. An oxygen electrode for a hydrogen ion cell comprising a tungstenelectrode and in contact therewith a mixture of different metallic solidoxides.

26. An oxygen electrode for a hydrogen ion cell omprlsing an electrode,and adjacent said electrode a mixture of different metallic solid oxidesof a metal or metals different from said electrode. t a

27. oxygen electrode for a hydrogen ion cell comprising a tungstenelectrode and in contact therewith a mixture of different other thantungsten.

28. A hydrogen ion cell comprising an electrode eflectin potentialsdependent upon "hydrogen ions, and a constant half cell comprising ametallic electrode, and a solution in which said metallic electrode isimmersed having a definite concentration of ions of the metal of saidelectrode.

29. A h drogen ion cell comprising an electrode e ecting potentialsdependent upon concentrations of hydrogen ions, and a constant half cellcomprising a copper electrode, and a solution in which said copperelectrode is immersed having a definite concentration of copper ions. e

30. Apparatus for utilizing or determining hydrogen ion concentrationscomprising a chamber, an electrode therein, means for passing'a solutionthrough said chamber, and a conduit through which solution is dischargedfrom said chamber, and a half cell comprising a second chambercommunimetal or metals cating with said conduit through a restrictedoutlet, an electrode in said second chamber and means for delivering aliquid to said second chamber ,9

' HENRY C. PARKER.

